Photographic filters have been used since the early times of photography, when subsequent processing of photos was impossible or very difficult. The role of filters in “classic” photography (on film) is undeniable. On the other hand, at present, many may think that the time of filter use is long gone, but they can’t be more mistaken. Perhaps, when hearing about filters, most people have photo-editing programs in mind, the various effects that can be applied with these, and the fast results that can be obtained by simply pressing some buttons on the screen. However, any serious discussion on photography eventually arrives at the issue of filters, and a serious photographer will carry a minimal set of filters in his bag to help him get better pictures in different circumstances.
If you still have doubts, you should know that there is a number of photographic filters whose effects cannot be reproduced using photo-editing programs. Of these, the polarizing filter is probably the most widely used.
Given the rather vague information on the subject that I was able to spot around the ‘net, I decided to write this crash course on the use of these essential accessories in the photographer’s toolbox: the photo filters. It is the first article in a series addressed to both amateur photographers and advanced, in which I’ll present the types of filters and their applications in photography.
What is a photo filter?
First of all, if I were to attempt a definition of a photo filter, it would sound something like this: a photo filter is a glass (or plastic) component which attaches in front of the camera lens with the goal to change the properties of light and thus, change the way the camera perceives and records the finished image.
Photo filters are, broadly, of two types: circular screw-on filters, and mounted ones, more commonly known by the brand that invented this model: Cokin Filters.
Circular screw-on filters are intended for use on the lenses they were designed for. These filters are picked by lens diameter. Very popular are the 77mm filters, due to professional lenses that have this standard diameter of their thread. Others may be of 55mm, 67mm, 82mm etc.
So, when you buy a screw-on filter, you must make sure that the diameter of the filter corresponds to that of the lens that will hold it.
“Mounted”, or Cokin filters as they are called, are, at first glance, more difficult to use than the screw-on ones. However, due to the fact that they are not designed to fit just a single lens diameter, Cokin type filters have the advantage of allowing to be mounted on the entire collection of lenses that you own. Using a system of adapter rings of various diameters, one Cokin filter becomes compatible with a large array of lenses. The filters of this type have become very popular because of their versatility and their reduced operating costs: you no longer have to buy extra filters of the same type in different diameters, since a Cokin filter fits on all the lenses that you own.
Classification of filters by the effect obtained
A classification of photo filters the effect they produce is as follows:
- UV, Skylight Filters
- Polarizing filters
- Neutral density and graduated (gray) filters
- Filters for photography in the IR range
- Filters for ultraviolet photography
- Colored filters, filters for special effects
I’ll present them one at a time, depending on their type and I’ll begin today with the first three categories. In a future article I’m going to write about the rest of the filters listed above.
UV, Skylight Filters
UV filters are generally completely transparent. Skylight filters have a yellowish tint, easily perceivable with the naked eye. Both types of filters are used to reduce the UV rays in the atmosphere, thus helping to take clear shots, without the haze common at high altitudes. Speak of high altitudes, it should be noted that these filters have no effect at heights in excess of 4500 feet/1500 meters or on the beach, where the Sun’s rays are strongest. Apart from this, they can be used as permanent protective filters for the front lens.
From this point of view many photographers (even professionals) recommend the use of screw-on UV filters as a method of protection. It is more convenient to hit or scratch a filter than a lens that’s a few dozen times pricier.
However, a word of advice on any type of filter: filters reduce image quality due to interposing a new layer of glass between your camera’s sensor and the subject being photographed. In the case of UV/protection filters, if they are of good quality, the impact over the image will be negligible and that’s why they are preferred, because of the protection offered.
Polarizing filters are designed to filter incident light by reducing or even eliminating glare. Thus, they increase clarity and enhance the colors and contrast of the image. Polarizing filters are useful in landscape photography, where they enhance the general contrast and the color of the sky. If the photo was taken through a glass window or any other medium that reflects light, the picture will be clearer and with better contrast. A polarizing filter can be used to reduce the amount of light that reaches the sensor, thus replacing a neutral density (ND) filter.
When using polarizing filters, keep in mind that they lower exposure by up to two or three positions. You’ll have to adjust exposure up to compensate for the decrease in the amount of light reaching the sensor, that results from using the filter.
Polarizing filters are of two kinds: circular and linear. For cameras with auto-focus, the use of Circular Polarizer filters filters is recommended, since the linear ones can confuse the automatic focus system.
When choosing a polarizing filter, one also needs to take into account the thickness of the glass that it’s made of. A thick polarizing filter will reduce even more the amount of light reaching the sensor, with a decrease in image quality, and with the production of a darkening of the corners (vignetting), which is more pronounced in the situation of the use a wide-angle lens. This is an important issue to keep in mind when using a polarizing filter for landscape photography, in order to prevent the alteration of the sky’s color across the entire frame, because of the use of the filter.
In the use of a polarizing filter it is necessary, before triggering, to rotate the filter until the colors and contrast are optimal. The effects of a polarizing filter can be seen immediately in the viewfinder or LCD screen, and that’s why their use is very simple.
Polarizing filters are very useful and recommended in many shooting situations. For many photographers, a polarizing filter is an accessory that’s never missing from their bag.
Neutral density (ND) and graduated (light gray) filters
Neutral density filters are designed to reduce the amount of light reaching the camera sensor, without affecting the colors in the photo. These are of two kinds: uniform filters and graduated filters (“two-tone”).
Uniform neutral density filters reduce the amount of light evenly on the entire surface of the filter. These are useful in landscape photography, where you’d otherwise need to expose very briefly. They are often used to highlight motion effects, the flow of water, etc.
Graduated filters reduce the amount of light in a different way because they are covered with a gray layer unevenly. These filters have their upper part greyed-out, while the lower part is clear. Usually the transition between the two parts is through a gradient area (hence the name ‘graduated or gradual filters‘). This type of filter is very useful when a part of the frame is brighter than the rest. In landscape photography, it often happens that the upper part of the image with the sky is over-exposed, or the bottom is under-exposed. The balance between the two areas can be obtained using a graduated filter that will reduce the amount of light in the upper area (sky) and will leave the lower area at the normal level. That way you can keep details across the entire frame, without any burned out area.
Tips for purchasing
When you buy a photo filter it’s recommended to keep in mind the following tips:
1) Check the compatibility of the filter with the lens. This is true for both screw-on filters and Cokin types. With screw-on filters thread, making a match is obvious – the filter diameter must be the same as the lens diameter, which is usually marked on the rim of the front lens. With Cokin filters, you must keep in mind the physical size of the filter, because the Cokin P system for instance supports objectives with 77mm maximum diameter. If you want support for larger diameter lenses, you will need to choose the Cokin X-PRO system, which uses larger holders and larger filters.
2) Check that the filter does not produce unwanted effects. If the filter is made of thick glass it is possible that it creates a vignetting effect on the image. In the case of wide-angle lenses, it’s preferable to buy a filter made from thinner glass (“low profile” – LPF la Hoya), to obtain a better quality towards the corners of the image.
3) Optical quality of the filter. Make sure the filter is made from quality glass and is produced by an established brand (B+W, Hoya, Cokin, Lee, etc.). A low quality filter can cause more harm than good.
4) Anti-reflective coating. Although more expensive, filters with multi-layered anti-reflective treatment are better because they reduce or even eliminate the risk of reflection.
5) Try not to combine filters excessively. You can combine filters, meaning you can use more than one filter at the same time, but this is not recommended because of the increased chance to get reflections, and because you’ll most likely get a lower image quality due to adding several layers of glass in front of the lens. Generally speaking, remember the rule: Any extra filter reduces image quality.
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